Milo g-



(No Model.)

M. G. KELLOGGK MULTIPLE SWITGHBOARD.

NO. 592,339 Patented 0013. 26,1897.

Subscriber No. 2 C 6 b b N l L/ 5C' er CY 6l, a', l L Z i 1 lin-.mg I h J 7L MEIN J' 7L 770 Q J/ Ira/falaz' Nrrn STATES ATnNT rrrcn.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO TIIE KELLOGG SIVITCIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

SPECIFICATION forming part of Letters Patent No. 592,339, dated October 26, 1897.

Application med December 20,1889. sei-a1 No. 334,357. da moda) To @ZZ whom t may concern:

Be it known that I, MILo G. KELLOGG, of Chicago,Illinois, temporarilyresiding at Stuttgart, in the Empire of Germany, have invented cert-ain new and useful Improvements in Multiple Switchboards for Telephone-Exchanges, of which the following is a full, clear, concise, and eXact description, reference being had to the accompanying drawing, forming a part of this specification.

My invention relates to a telephoneexchange system in which the subscribers lines are metallic-circuit lines; and it consists in a system of calling, switching, and testing such lines which I shall describe and claim.

I place as many switchboards in the central oflice as are found necessary or desirable in order to properly answer the calls and connect and disconnect the subscribers lines. O11 each board I place for each line a springjack or similar switch having two contactpieces which are normally in contact and a third contact-piece normally insulated from the rest, (except by the circuit connections,) said switch being adapted to receivea switchplug, and when a plug is inserted to disconnect the contact-pieces of the switch which are normally in contact and connect one of them with one contact-piece of the plug, While the other contact-piece of the plug is connected with said third contact-piece of the switch. The third contact pieces of the switches mentioned above are so placed and arranged that the operator may at will apply a test-plug or similar device to them.

In the drawing the iigure represents the apparatus and circuits embodying one form of my invention.

Two metallic circuits are shown connected to two boards A and B of a multiple-switchboard exchange. Each of the metallic circuits may be traced from the test-contacts j in the spring-jacks l) CL and b a over the line conductor T to the subscribers station, thence to the telephone 4 and secondary coil 7 of the induction-coil to the switch-lever l, short-circuited by the conductor 10 and contact 9 normally or when the telephone is not switched for use, thence through the primary coil 6, bells 2, to the generator-fra1ne 3, thence through the armature of the generator by way of conductor l5 to the line conductor S, through normally closed contacts g h, annunciator w, common wire C, thence back to the subscribers station to contacts r, adapted to be connected to the generator-contact p, while callin g by the usual automatic device. Vhen the telephone 4 is removed from its hook l, the bells 2 and generator 3 are short-circuited by the conductor 13 and contact 1l. At the same time the transmitter-circuit is closed from the switch-lever l through the primary coil 6, transmitter 5, battery 8, and contact l2. The short circuit 14E and the normally closed contacts p q switch the armature from the circuit except when the generatoiris actuated for a call, when these contacts are opened for calling by the automatic device already referred to.

Each spring-jack a b a h' is provided with a switch-hole Z and is provided with Vnormally closed contacts g h, disconnected by a switchplug D or D when inserted therein, and a test-contactj, placed, as shown, so that a testplug T can be applied to it for testing.

When a subscribers call-generator is actuated, the following call-circuit is established: generator-contactp, the armature of said gen erator, the conductor l5, line conductor S, annunciator w, and common return-conductor C, to the contact r, connected to the generator-contact p while calling.

At each board is located an operators test outfit comprising a test-plug T, a test receiving instrument t'-a telephone, for exampleand a test-battery B, all connected to the common wire C. Instead of a separate battery B for each outt there may be a single testbattery B3. (Shown in broken lines.) When a test-plug Tis applied to a test-contact ,j for testing, a test-circuit is established from the test-contact j over the two line conductors '1" and S, including the subscribers outfit and the normally closed contacts g h, thence through the annunciator w, common wire C, to the test outfit. This circuit is shown over line No. l.

At board A the operators outt is shown testing line No. 2. As the contacts g h of spring-jack b at board B are opened by the switch-plug D no test-circuit is established. IVheu a circuit is closed, the current from lCO the test-battery causes a click in the telephone, indicating that the line is free. When, however, no test-circuit is established, the test receiving instrument will remain silent. This indicates that the line is busy.

At board B is shown an operators switching outfit comprising two switch-plugs D and D. Each plug is composed ofinsulating material m, upon which are mounted two contacts 'n and n', adapted to be connected to two jackcontacts j and g when inserted in a jack and adapted to be cross-connected by the conducting base-plate o when in their normal position.

The two contacts n of the two switch-plugs are connected together by a flexible conductor d. The two contacts n are connected together by a flexible conductor d, in the circuit of which is a looping-in switch Y, adapted to be placed upon pairs of contacts q q', fl" r', or s s', and thereby loop into the circuit a call-generator B2, an operators telephone set t, or a clearing-out annunciatorc. When one plugisinserted in a spring-j ack, as shown at board B, the circuit' of the operators apparatus is completed through the cross-connected contacts of the other plug.

The operation of the system is as follows: When a subscriber desires to call, he turns the crank of his generator, thereby removing the shunt and connecting the line with the common wire, so that the armature-coil is between this connection and the line-annunciator. A complete circuit being thus established, in which is the armature-coil and the annunciator, the latter indicates a call. The operator then places one of a pair of plugs into the switch of the line indicated, and by conversation finds out what line iswanted.

' She then tests the line wanted by placing the test-plug on the'contact-piece j of its switch. If the line is not switched for use, a complete circuit will be established, in which is the operators test receiving instrument and battery, and the test receiving instrument will respond. If, on the other hand, the line is switched for use by a plug being in one of its switches, the circuit, as above described, will be open and the instrument will not respond. The operator can therefore determine on testing whether or not a line is in use.

When the test indicates that the line is not in use, the operator will place the other plug voi' the pair in the switch of the called line.

The two lines are thus connected together in metallic circuit, and their normal connection with the common wire is removed. The operator may now by moving the levers of the looping-in switch connect her calling-generator into the circuit. Again, she may by moving the levers of the switch connect a clearing-out annunciator into the circuit. Again, she may by moving the levers of' the switch loop her telephone into the circuit and listen to determine whether the subscribers are through conversation.

By this system of calling, switching, and testing the test receiving instruments are not 4when it was switched at the central ofiice, as

. would be liable to be lthe case were the test receiving instrument connected with the ground. It is well known that such accif, dental grounds are liable to occur, and it is apparent that inthe system described above such a ground would not affect the testing or other operation ot the system.

Normally the looping -in switch Y rests upon the annunciator-contacts s s. Ifplaced upon other contacts while the switching sysl tern is not in use-the telephone or generator Q contacts, for example-those elements would `be short-circuited and rendered useless for the other plug sets.

The annunciators w are distributed among the various boards to equalize the work of the various operators.

Vhat I claim, and desire Letters Patent for, is-' l. In a multiple-switchboard exchange, a three-conductor system comprising a telephone-circuit, ungrounded call and testcircuits associated therewith, each extending from the subscribers station to the central office, one conductor and one only common to both circuits.

2. Inamultiple-switchboard exchange, ungrounded telephone, call and test circuits, each extending from the subscribers station to the central oftice, a conductor common to each of. said circuits, asecond conductor common to said telephone and test circuits, and a third conductor forming a part of said callcircuit, each conductor electrically continuous from the subscribers stationto the central office. y

3. Inamultiple-switchboard exchange, ungrounded telephone, call and test circuits, each extending from the subscribers station to the central ottice, a conductor common to each of said circuits, a second conductor common to said telephone and test circuits, and a third conductor forming a part of said callcircuit, each conductor electrically continuous from the subscribers station to the central office, said circuits being normally open but closed while performing their several functions.' K

4. In amultiple-switchboard exchange, a telephone-line, ungrounded call and test circuits associated therewith, three conductors each extending from the subscribers station to the central office, a single conductor common to both including a call device and nor-- mally closed contacts open while the telephone-line is switched for use, a call-generai tor in said call-circuit, and a test-battery in said test-circuit at the central station.

5. In a multiple-switchboard exchange, un-

three conductors each extending from the IOO IIO

subscribers station to the central ofce, a

conductor common to said call and test circuits, a second conductor common to said test and telephone circuits, a third conductor forming part of said call-circuit, and a test battery and instrument in said test-circuit at the central station.

6. In a multipleswitchboard exchange, ungrounded telephone, call and test circuits, three conductors each extending from the subscribers station to the central office, normally open but closed While performing their several functions, a conductor common to said call and test circuits, a second conductor common to said test and telephone circuits, a third conductor forming part of said callcircuit, and a test battery and instrument in said tcst-circuit at the central station.

7 In a multiple-switchboard exchange, in the order named, test-contacts, an ungrounded metallic circuit closed at the subscribers station ,normally closed switchboard-contacts opened While in use,a call-annunciator, an ungrounded conductor, an extension to the subscribers station including normally open contacts closed through a call-generator While calling; in combination with a test outfit including a test-battery connected on one side to said ungrounded conductor and on the other side adapted to be connected to a testcontact for testing.

8. In a multiple-switchboard exchange, in the order named, test-contacts, one at each board, a line-conductor, an ungrounded su bscribers outfit including a call-generator, a

return line conductor, normally closed -jackcontacts, a pair at each board opened while the line is switched, for use, an annunciator and two connections, one to an ungrounded common conductor adapted to be connected to a subscribers call-generatorwhile calling; the other to an operators test outfit including a test-battery, adapted to be connected to a test-contact for testing.

9. In a multiple-switchboard exchange, two metallic circuits, each connected in the order named from test-contacts, one at each board, a line conductor, ungrounded subscribers outfit including a call-generator, a return line conductor, normally closed jack-contacts, a pair at each board opened while the line is switched for use, an annunciator, and two connections one to an ungrounded common conductor adapted to be connected to a MILO G. KELLOGG- Witnesses EMIL ABENHEIM, MARGARETHA RIEHL. 

